// CSparse/Source/cs_fkeep: keep or drop entries from a sparse matrix
// CSparse, Copyright (c) 2006-2022, Timothy A. Davis. All Rights Reserved.
// SPDX-License-Identifier: LGPL-2.1+
#include "cs.h"
/* drop entries for which fkeep(A(i,j)) is false; return nz if OK, else -1 */
csi cs_fkeep (cs *A, csi (*fkeep) (csi, csi, double, void *), void *other)
{
    csi j, p, nz = 0, n, *Ap, *Ai ;
    double *Ax ;
    if (!CS_CSC (A) || !fkeep) return (-1) ;    /* check inputs */
    n = A->n ; Ap = A->p ; Ai = A->i ; Ax = A->x ;
    for (j = 0 ; j < n ; j++)
    {
        p = Ap [j] ;                        /* get current location of col j */
        Ap [j] = nz ;                       /* record new location of col j */
        for ( ; p < Ap [j+1] ; p++)
        {
            if (fkeep (Ai [p], j, Ax ? Ax [p] : 1, other))
            {
                if (Ax) Ax [nz] = Ax [p] ;  /* keep A(i,j) */
                Ai [nz++] = Ai [p] ;
            }
        }
    }
    Ap [n] = nz ;                           /* finalize A */
    cs_sprealloc (A, 0) ;                   /* remove extra space from A */
    return (nz) ;
}